The defect chemistry of UO2±x from atomistic simulations

Cooper, M.W.D. and Murphy, S.T. and Andersson, D.A. (2018) The defect chemistry of UO2±x from atomistic simulations. Journal of Nuclear Materials, 504. pp. 251-260. ISSN 0022-3115

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Abstract

Control of the defect chemistry in UO2±x is important for manipulating nuclear fuel properties and fuel performance. For example, the uranium vacancy concentration is critical for fission gas release and sintering, while all oxygen and uranium defects are known to strongly influence thermal conductivity. Here the point defect concentrations in thermal equilibrium are predicted using defect energies from density functional theory (DFT) and vibrational entropies calculated using empirical potentials. Electrons and holes have been treated in a similar fashion to other charged defects allowing for structural relaxation around the localized electronic defects. Predictions are made for the defect concentrations and non-stoichiometry of UO2±x as a function of oxygen partial pressure and temperature. If vibrational entropy is omitted, oxygen interstitials are predicted to be the dominant mechanism of excess oxygen accommodation over only a small temperature range (1265 K–1350 K), in contrast to experimental observation. Conversely, if vibrational entropy is included oxygen interstitials dominate from 1165 K to 1680 K (Busker potential) or from 1275 K to 1630 K (CRG potential). Below these temperature ranges excess oxygen is predicted to be accommodated by uranium vacancies, while above them the system is hypo-stoichiometric with oxygen deficiency accommodated by oxygen vacancies. Our results are discussed in the context of oxygen clustering, formation of U4O9, and issues for fuel behavior. In particular, the variation of the uranium vacancy concentrations as a function of temperature and oxygen partial pressure will underpin future studies into fission gas diffusivity and broaden the understanding of UO2±x sintering.

Item Type:
Journal Article
Journal or Publication Title:
Journal of Nuclear Materials
Additional Information:
This is the author’s version of a work that was accepted for publication in Journal of Nuclear Materials. Changes resulting from the publishing process, such as peer review, editing, corrections, structural formatting, and other quality control mechanisms may not be reflected in this document. Changes may have been made to this work since it was submitted for publication. A definitive version was subsequently published in Journal of Nuclear Materials, 504, 2018 DOI: 10.1016/j.jnucmat.2018.02.034
Uncontrolled Keywords:
/dk/atira/pure/subjectarea/asjc/3100/3106
Subjects:
ID Code:
123888
Deposited By:
Deposited On:
07 Mar 2018 12:00
Refereed?:
Yes
Published?:
Published
Last Modified:
15 Jul 2020 07:45